In the completion of underwater oil and gas wells, it is frequently necessary to suspend in a single borehole a plurality of strings of pipe which extend side-by-side rather than concentrically. Thus, in the case of an underwater well in which the borehole traverses two separate producing strata, a first tubing string extends to the lowermost strata, a second tubing string extends to the superadjacent strata, and the space within the innermost casing is sealed off between the two strata. In such an installation, one or more hydraulic lines, typically lines to control downhole safety valves, must be suspended beside the tubing strings. In typical wells, the length of the tubing strings may be quite great, so that the total weight of the strings to be suspended may be 300,000 pounds or more. In most underwater wells, the multiple strings of pipe are suspended from a single support, typically a tubing hanger, seated on a shoulder in the well structure near the bottom of the body of water in which the well is installed. Installation of the multiple strings of pipe is accomplished from an operational base, such as a vessel or a platform, located at the surface of the body of water. Thus, in installing a plurality of tubing strings, the last joints of the tubing strings are attached to a tubing hanger by direct manual steps taken on the operational base. Then, the tubing hanger is attached to a handling tool, the handling tool is attached to a handling string, and the final stages of running the tubing strings into the well, plus the step of landing the tubing hanger, are accomplished from the operational base by manipulating the handling string.
The water depths involved are usually quite great, typically well beyond the depths at which divers can operate, and all operations are therefore carried out with the aid of a guidance system, typically a plurality of guide lines extending from the operational base to upright guide posts carried by a guide means base centered on the borehole at the bottom of the body of water. The guidance system serves not only to guide all of the well components into a position, e.g., precisely centered on the borehole but also to provide an orientation reference for those elements which must, once installed, occupy a known rotational position. Thus, a tubing hanger supporting two strings of tubing side-by-side presents two upwardly opening bores, each of which communicates with a different one of the tubing strings, and each of which must receive, e.g., a different one of two stingers carried by the production upper body when that body is installed. Since a component such as the production upper body is installed after the tubing hanger is installed, it is apparent that a multiple string tubing hanger must be landed in a known rotational position relative to the guidance system, else the production upper body cannot be mated successfully with the tubing hanger. And landing of the hanger in a known rotational position must be accomplished remotely, by operations carried out from the surface of the body of water.
Prior-art workers have generally attacked this set of problems by providing a wellhead or other well structure at or near the floor of the body of water with a tubing hanger support, which may be a shoulder presented by a casing hanger, providing an upright passage above the tubing hanger support, providing a rotational orientation reference such as a vertical slot in the upright passage, using a handling tool to manipulate the tubing hanger, and equipping the handling tool with locator means which can be made to coact with the rotational orientation reference, when the handling tool is rotated by manipulating the handling string. To aid in rotation of the combination of the handling tool, tubing hanger and tubing strings, various bearing arrangements have been proposed. Thus, bearings have been provided which are interposed between the tubing hanger and its support, as seen in U.S. Pat. No. 3,688,841, issued Sept. 5, 1972, to Benton F. Baugh, and pending application Ser. No. 36,659, filed May 7, 1979, by Michael L. Wilson. However, such approaches, at least in some cases, have the deficiencies that the bearing must be provided in a part of the structure which affords little room to accommodate the bearing, that the location of the bearing requires modification of the tubing hanger itself, so as to provide bearing races, that the area occupied by the bearing is one in which effective seals must be provided to act against downhole pressures, and that the size limitation may now allow use of a standard bearing. In other prior-art proposals, such as that seen in U.S. Pat. No. 3,693,714, issued Sept. 26, 1972, to Benton F. Baugh, the bearing is provided between the handling tool and a tubular member carried by the handling tool disposed to engage the casing hanger or other element which is to support the tubing hanger, the tubing hanger being released and lowered for landing after rotational orientation has been accomplished. Though this latter approach has the advantage that the entire weight of the tubing strings, tubing hanger and handling tool is supported by the bearing before the tubing hanger is landed, it has in general the same deficiencies that are encountered when the bearing is interposed directly between the tubing hanger and its support.
While such prior-art approaches have achieved considerable success and acceptance in the field, there has been a continuing need for improvement.